The || operator returns true if either side is true. You use this when any of several conditions should trigger an action. if (x < 0 || x > 10) executes when x is outside the range 0 to 10.
OR allows multiple valid conditions. if (day == 0 || day == 6) checks if day is Sunday or Saturday. Only one needs to match for the whole expression to be true. When combining AND and OR, use parentheses for clarity.
if ((x > 0 && x < 10) || x == 100) allows x in 1-9 or exactly 100. Without parentheses, precedence rules might surprise you.